Owing to aging of the population and an increase in health conscious, medical instruments are essential for our life. Particularly, a magnetic resonance imaging (MRI) technique which gives no damage to a human body and can obtain a tomographic image in the body which cannot be normally visualized, strongly attracts attention in diagnosis in the super-early stage of diseases including cancers.
In MRI diagnosis of diseases, abnormal cells causing diseases are specifically labeled, distinguished from normal cells by the labeling, and imaged. Abnormal cells can be labeled by using, for example, expression of specific genes and proteins, accumulation of metabolites, or the like as an indicator. Particularly, it can be said that since the genes are expressed at a position in an uppermost stream stage of a disease process, the gene expression is the most suitable indicator for diagnosis in the early stage.
One of the methods of labeling abnormal cells using such a gene expression as an indicator is a method of using a reporter gene. In the method, the reporter gene is linked to a downstream of a promoter region of a gene serving as an indicator. When the promoter is activated in an abnormal cell, the reporter gene at the downstream of the promoter is expressed. The cell is directly or indirectly labeled with a product of the expressed reporter gene. As a typical example of the reporter gene, a gene for green fluorescent protein (GFP) to fluorescently label cells is cited. The fluorescently labeled cells are imaged by a device equipped with a fluorescence microscope system.
Some of the reporter genes developed for MRI have been reported. Examples thereof include iron-binding proteins such as ferritin and transferrin. These are an iron-binding reporter gene. The iron-binding reporter gene accumulates iron in a cell in which the iron-binding reporter gene is expressed. The accumulation allows the cell to be labeled with iron. Since an iron imaging effect can be utilized in MRI imaging, a cell labeled with iron accumulated in the cell is detected by the T1- and T2*-weighted image of MRI.
Under such circumstances, in order to achieve an earlier diagnosis, there is a strong demand for development of highly sensitive diagnosis.